The work proposed is an attempt to understand the local mechanisms involved in the regulation of meiosis in mammals. It is suggested that meiosis is held in the arrested diplotene condition as the result of intimate cell contacts between the cornona cells and oocyte. It is proposed to analyze these relations in detail by ultrastructural studies. Electronprobe microanalysis will be used to determine the nature of the ionic environment in the neighborhood of the oocyte during maturation by the analysis of microsamples of antral fluid. These results will be used to help develop a "mini-organ culture" system for the cumulus oophorus which remains in a quiescent stage until stimulated by LH. This preparation will be used for more detailed studies on the regulation of meiosis in mammals.